1. Field of the Invention
The present invention relates to a video tape recorder (VTR) and, more particularly, to a video tape recorder (VTR) which is suitable for recording a digital image signal and a digital audio signal on a magnetic tape.
2. Description of the Related Art
In some conventional digital video tape recorders (digital VTRs) which record and reproduce a digital image signal, as shown, for example, in FIG. 1, a recording signal S.sub.REC is sequentially recorded with the aid of a recording head 4A on a magnetic tape 1 that runs in the direction indicated by arrow K1. This recording signal S.sub.REC is sent from a recording circuit 3, and is composed of a digital image signal and a digital audio signal. A reproducing signal S.sub.PB which is read with the aid of a reproducing head 5A arranged downstream of the magnetic tape 1 is reproduced by a reproducing circuit 6 immediately after the recording signal S.sub.REC has been recorded. The digital signal can thus be monitored to determine whether or not it has been recorded correctly.
A VTR has been proposed (refer to Japanese Unexamined Publication No. 56-156975) in which, during reproduction, a reproduced signal is first stored, and a pre-existing signal recorded on a magnetic tape is deleted. The reproduced signal which has been recorded is then written once again.
As shown in FIG. 2, tracks TR1, TR2 . . . are sequentially arranged on the magnetic tape 1 to be apart from each other at a distance equal to a track pitch TP. The six tracks TR1-TR6 out of the above plurality of tracks are regarded as being one set. The digital image signal and the digital audio signal equal to the amount of one field are divided into and recorded on the six tracks TR1-TR6.
Each of the six tracks TR1-TR6 is divided into a region ARV (called an image region) in which the digital image signal is recorded and a region ARA (called an audio region) in which the digital audio signal is recorded.
As illustrated in FIG. 3, the image region ARV is subdivided into k recording regions (called sync blocks) SBVl-SBVk. A synchronization pattern, an ID pattern, a data block and error controlling data are recorded in each sync block.
Furthermore, as shown in FIG. 4, the audio region ARA is divided into four channel regions ARA1-ARA4. Each channel region is further subdivided into n sink blocks SBAtl-SBAtn (t=1, 2, 3 and 4) in the same manner as in the image region ARV. The data of a 4-channel digital audio signal is assigned to and recorded in each channel region.
A rotary drum 7 having the construction shown in FIG. 5 is used in a digital VTR in which the digital image signal and the digital audio signal, utilizing the formats mentioned above, are recorded and reproduced on the magnetic tape 1.
That is, the rotary drum 7 has the magnetic tape 1 wound around the periphery 7A of the rotary drum 7 by guide posts 8A and 8B. The magnetic tape 1 runs in the direction indicated by arrow K1, whereas the rotary drum 7 rotates in the direction indicated by arrow K2.
The rotary drum 7 is provided with a total of four recording/reproducing systems which are all similar to a first recording/reproducing system. This first recording/reproducing system is composed of the recording head 4A and the reproducing head 5A, both of which were previously described with reference to FIG. 1.
In other words, the first recording/reproducing system (see FIG. 1) is constructed in such a way that the recording head 4A, for scanning the track TR1 (see FIG. 2), is arranged on the periphery 7A of the rotary drum 7. The reproducing head 5A, for reproducing and scanning the track TR1 after the recording head 4A has scanned, is also disposed in the direction opposite to that in which the rotary drum 7 rotates, 90.degree. apart from the recording head 4A.
A recording head 4B and a reproducing head 5B, both of which are used for sequentially scanning the track TR2 and which act as a second recording/reproducing system, are disposed apart from the recording head 4A and the reproducing head 5A, respectively, at a distance equal to only the track pitch TP.
A recording head 4C and a reproducing head 5C, both of which serve as a third recording/reproducing system and are used for sequentially scanning the track TR3, are further arranged 180.degree. apart from the recording head 4A and the reproducing head 5A, respectively. Also, a recording head 4D and a reproducing head 5D, both of which are used for sequentially scanning the track TR4 and which serve as a fourth recording/reproducing system, are disposed apart from the recording head 4C and the reproducing head 5C at a distance equal to only the track pitch TP.
The rotary drum 7 thus has four recording/reproducing systems. While the rotary drum 7 rotates a half turn, the recording heads 4A and 4B record and scan the tracks TR1 and TR2. Thereafter, while the rotary drum 7 rotates another half turn, the recording heads 4C and 4D record and scan the tracks TR3 and TR4. While the rotary drum 7 further rotates a half turn, the recording heads 4A and 4B record and scan the tracks TR5 and TR6.
Thus, every time the rotary drum 7 rotates one and a half turns, the digital image signal and the digital audio signal equal to the amount of one field are sequentially recorded on the tracks TR1-TR6.
On the other hand, the reproducing heads 5A and 5B follow and scan the tracks TR1 and TR2 which have been scanned by the recording heads 4A and 4B. These reproducing heads 5A and 5B reproduce and monitor the recording signal which has been recorded by the recording heads 4A and 4B immediately after the recording heads 4A and 4B have recorded the recording signal. Similarly, the reproducing heads 5C and 5D follow and scan the tracks TR3 and TR4 which have been scanned by the recording heads 4C and 4D. The reproducing heads 5C and 5D reproduce and monitor the recording signal which has been recorded by the recording heads 4C and 4D immediately after the recording heads 4C and 4D have recorded the recording signal.
Thus, the recording heads 4A-4D sequentially record the digital image signal and the digital audio signal on the tracks TR1-TR6 of the magnetic tape 1. The reproducing heads 5A-5D subsequently detect whether or not the digital image and digital audio signals are recorded correctly.
In the thus-constructed digital VTR, the recording heads 4A-4D scan the magnetic tape 1 while slidably coming in contact with the surface of the magnetic tape 1. In such an arrangement, a foreign substance such as dust may get caught in the gaps (head gaps) between the magnetic tape 1 and the recording heads 4A-4D. This results in a problem in that what is called a dropout occurs in which the recorded data is partially missing. A foreign substance such as dust may also get caught in the head gaps, thus leading to a problem in that what is known a clog occurs in which the recorded data is continuously missing. Such problems deteriorate the reproduced image and sound.